The permeability of ferromagnetic materials is influenced by mechanical strains. This physical effect, which is known as the magnetoelastic effect, can be utilized for measuring torque in a rotating object, since a torque creates strains in the rotating object. A series of different sensors are known which make use of the magnetoelastic effect in order to detect torques, of shafts for example, in a non-contact manner. The magnetoelastic sensors are characterized by their high accuracy, wherein a recalibration is required just as little as movement towards reference marks.
A magnetoelastic torque sensor, which is used for measuring the torque of drive shafts, is known for example from DE 10 2009 008 074 A1. This document describes a measurement arrangement for detecting the torque of a shaft, which includes a torque sensor positioned with a prespecified gap from the surface of the shaft.
To measure torques on force-transferring shafts of machines, an electromagnetic coil is arranged at a small distance from the surface of the shaft without being in contact with it, which reacts to the change of permeability in a ferromagnetic layer on the shaft or a ferromagnetic shaft per se with a change in its signal. For this purpose the shaft must be subjected to torsional strains, i.e. the magnetoelastic torque sensor must be arranged along the shaft between a driving torque and the opposing reaction torque acting against it. This means that the shaft formed from the ferromagnetic material is part of the measurement apparatus.
If positional changes of the shaft occur during the measurement the measurement result, which reacts very sensitively to the distance between the sensor and the shaft, will be influenced by the position changes. Movements by few tenths of millimeters perpendicular to the axis of rotation of the shaft already reduce the measurement accuracy of the torque sensor significantly. Especially with technical applications in which shafts with large dimensions are used for force transmission, such positional changes of the shaft cannot be rectified with an economically justifiable technical effort. It has therefore been proposed in DE 10 2009 008 074 A1 that the torque sensor be positioned on the shaft by means of a ring surrounding said shaft. The ring is also connected to a housing section to prevent it from rotating along with the shaft. In this case it is able to be pivoted around a pivot axis and is attached movably to the housing section in the radial direction of the shaft, so that it can make the same movements as the shaft. In such cases the ring is supported on the shaft by a support bearing, by shell bearings or by roller bearings.
In the light of the prior art described, the object of the present invention is to make available an advantageous torque sensor arrangement with a non-contact torque sensor. A further object of the invention is to make available an advantageous shaft.